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Elucidation of a [4Fe-4S] cluster degradation pathway: rapid kinetic studies of the degradation of Chromatium vinosum HiPIP. J Biol Inorg Chem 2001 Mar;6(3):266-74

Date

04/24/2001

Pubmed ID

11315562

DOI

10.1007/s007750000196

Scopus ID

2-s2.0-0034847133 (requires institutional sign-in at Scopus site)   9 Citations

Abstract

Irreversible disassembly of the 4Fe-4S cluster in Chromatium vinosum high-potential iron protein (HiPIP) has been investigated in the presence of a low concentration of guanidinium hydrochloride. From the dependence of degradation rate on [H+], it is deduced that at least three protons are required to trigger efficient cluster degradation. Under these conditions the protonated cluster shows broadened Mössbauer signals, but delta EQ (1.1 mm/s) and delta (0.44 mm/s) are similar to the native form. Collapse of the protonated transition state complex, revealed by rapid-quench Mössbauer experiments, occurs with a measured rate constant kobs approximately 0.72 +/- 0.35 s-1 that is consistent with results from time-resolved electronic absorption and fluorescence (kobs approximately 0.4 +/- 0.1 s-1) and EPR (kobs approximately 0.62 +/- 0.18 s-1) measurements. Apparently, guanidinium hydrochloride serves to perturb the tertiary structure of the protein, facilitating protonation of the cluster, but not degradation per se. Release of iron ions occurs even more slowly with kobs approximately 0.07 +/- 0.02 s-1, as determined by the appearance of the g = 4.3 EPR signal. Proton-mediated cluster degradation is sensitive to the oxidation state of the cluster, with the oxidized state showing a two-fold slower rate in acidic solutions as a result of increased electrostatic repulsion with the cluster. Consistent results are obtained from absorption, fluorescence, Mössbauer and EPR measurements.

Author List

Foster MW, Bian S, Surerus KK, Cowan JA

Author

Kristene K. Surerus in the Chemistry and Biochemistry department at University of Wisconsin - Milwaukee




MESH terms used to index this publication - Major topics in bold

Absorption
Bacterial Proteins
Chromatium
Electron Spin Resonance Spectroscopy
Iron
Iron-Sulfur Proteins
Kinetics
Oxidation-Reduction
Photosynthetic Reaction Center Complex Proteins
Spectrometry, Fluorescence
Spectroscopy, Mossbauer
Sulfur